Manufacture of nanocellulose and intermediates thereof

ABSTRACT

The present invention relates to a method for manufacturing nanocellulose comprising the steps of: a) providing a cellulose-containing material wherein the cellulose-containing material contains less than 20 wt. % water, b) contacting the cellulose-containing material with oxalic acid dihydrate, and heating above the melting point of the oxalic acid dihydrate, to obtain cellulose oxalates, c) washing the mixture, d) preparing a suspension comprising the washed material from step c) and e) recovering nanocellulose from the suspension. The present invention relates also to a method of manufacturing nanocellulose intermediate which comprises the above described steps a)-c). The methods disclosed in the present invention are quick, simple, and direct. Pulp can be used as raw material. A considerable amount of free carboxyl groups are introduced. A high yield can be obtained. The methods are inexpensive.

TECHNICAL FIELD

The present invention relates generally to nanocellulose as well as amethod for manufacturing nanocellulose. More specifically, the presentinvention relates to nanocrystalline cellulose and/or nanofibrillatedcellulose as well as methods for manufacturing nanocrystalline celluloseand/or nanofibrillated cellulose. Furthermore, the present inventionalso relates to nanocellulose intermediates as well as methods formanufacturing a nanocellulose intermediates.

BACKGROUND

Nanocellulose has driven increased attention over the last decade.Hitherto, the reported “main stream” methods for the preparation ofnanocellulose are generally categorized into 2 groups:

(1) preparation of nanocrystalline celluloses/cellulosenanocrystals/cellulose nanowhiskers by strong acid hydrolysis andthereafter mechanical disintegration (Rånby B. G. 1949. Aqueouscolloidal solutions of cellulose micelles. Acta Chemica Scandinavica 3:649-650. Dong X. M., Revol J-F. and Gray D. G. 1998. Effect ofmicrocrystallite preparation conditions on the formation of colloidcrystals of cellulose. Cellulose 5: 19-32. Beck-Candanedo S., Roman M.and Gray D. G. 2005. Effect of Reaction Conditions on the Properties andBehaviour of Wood Cellulose Nanocrystal Suspensions. Biomacromolecules6: 1048-1054.),

(2) preparation of nanofibrillated celluloses/cellulose nanofibrils bymechanical disintegration of cellulose directly (Turbak A. F., Snyder F.W. and Sandberg K. R. 1983. Microfibrillated cellulose, a new celluloseproduct: Properties, uses, and commercial potential. Journal of AppliedPolymer Science Applied Polymer Symposia 37: 815-827.), or celluloseafter enzymatic treatment (Henriksson M., Henriksson G., Berglund L. A.and Lindström T. 2007. An environmentally friendly method forenzyme-assisted preparation of microfibrillated cellulose (MFC)nanofibers. European Polymer Journal 43: 3434-3441.), or cellulose afterchemical treatments such as partial carboxymethylation (Wågberg L.,Decher G., Norgren M., Lindström T., Ankerfors M. and Axnäs K. 2008. Thebuild-up of polyelectrolyte multilayers of microfibrillated celluloseand cationic polyelectrolytes. Langmuir 24: 784-795.) or2,2,6,6-tetramethylpiperidine-1-oxy radical (TEMPO) mediated oxidation(Saito T., Kimura S., Nishiyama Y. and Isogai A. 2007. Cellulosenanofibers prepared by TEMPO-mediated oxidation of native cellulose.Biomacromolecules 8: 2485-2491.).

Abraham E., Deepa B., Pothan L. A., Jacob M., Thomas S., Cvelbar U. andAnandjiwala R. 2011. In “Extraction of nanocrystalline cellulose fibrilsfrom lignocellulosic fibres: A novel approach”. Carbohydrate Polymers86: 1468-1475 discloses a method of carrying out a mild acid hydrolysisof the agricultural sourced cellulose with 5% oxalic acid solution toprepare nanocrystalline cellulose, followed by harsh mechanicaldisintegration.

Gardea-Hernández G., Ibarra-Gómez R., Flores-Gallardo S. G.,Hernández-Escobar C. A., Pérez-Romo P. and Zaragoza-Contreras E. A.2008. In “Fast wood fiber esterification. I. Reaction with oxalic acidand cetyl alcohol”. Carbohydrate Polymers 71: 1-8 discloses a method formodifying wood fiber with non-solvent media, to produce ready-to-usehydrophobic fiber suitable for use in composites. Oxalic acid is used asan esterification agent for wood fiber.

Sirviö, J. A., Visanko, M. and Liimatainen, H. 2016 (published 1 Aug.2016). In “Acidic deep eutectic solvents as hydrolytic media forcellulose nanocrystal production”. Biomacromolecules 17: 3025-3032discloses a method of producing cellulose nanocrystals by using eutecticsolvents comprising oxalic acid dihydrate and choline chloride.

WO 01/02441 discloses production of microcrystalline cellulose. Pulp ishydrolyzed with active oxygen in an acidic environment. For instance,oxalic acid can be present. The pulp is treated in aqueous environment.

However, a considerable amount of water is normally used in theseprocesses as well as expensive processing reagents such as TEMPO andenzymes. These factors in total make the production of nanocellulose inlarger scale a costly process.

It is a problem that the production of nanocrystalline cellulose andnanofibrillated cellulose requires a lot of water and the productionyield is low, which make such process expensive.

SUMMARY

It is an object of the present invention to obviate at least some of thedisadvantages in the prior art and provide an improved method formanufacturing nanocellulose, i.e. nanocrystalline cellulose and/ornanofibrillated cellulose.

In a first aspect there is provided a method for manufacturingnanocellulose, said method comprising the steps of:

-   a) providing a cellulose-containing material wherein the    cellulose-containing material contains less than 20 wt. % water,    preferably less than 10 wt. % water,-   b) contacting the cellulose-containing material with oxalic acid    dihydrate, and heating above the melting point of the oxalic acid    dihydrate, to obtain cellulose oxalates,-   c) washing the mixture resulting from step b),-   d) preparing a suspension comprising the washed material from step    c), and-   e) recovering nanocellulose from the suspension, wherein said    nanocellulose is nanocrystalline cellulose.

In a second aspect of the invention there is provided a compositioncomprising nanocrystalline cellulose manufactured according to themethod disclosed in the first aspect of the invention.

In a third aspect of the invention there is provided a use of acomposition comprising nanocrystalline cellulose according to the secondaspect of the invention in at least one of: automotive bio-basedcomposites such as fiberglass replacement for structural andnon-structural uses, cement additives, wet-strength additives,dry-strength additives, wet-end additives such as wet-end additives inpackaging coatings and films, transparent films for food packaging,polymer composite additives in composites, paper, electronic packaging,pharmaceutical excipients such as fillers, paper composites withsuperior strength properties, hygiene and absorbent products,mechanically enhanced spun fibers and textiles, cosmetic excipients suchas filler, food additives, insulation for buildings such as sound and/orheat barriers, aerospace composites, aerogels for oil and gas, pigmentssuch as architectural pigments, coatings, hydrophobic and self-cleaningcoatings, paints, dispersants, viscosity modulators, building materialssuch as structural composites, switchable optical devices, bonereplacement, tooth repair medical composites, strain sensors, filterssuch as filtration of water and air, flexible displays, OLED displays,flexible circuits, printable electronics, conductive substrates, solarpanels such as flexible solar panels, smart packaging, photonics, anddrug delivery.

In a fourth aspect of the invention there is provided a method formanufacturing nanocellulose, said method comprising the steps of:

-   -   a. providing a cellulose-containing material wherein the        cellulose-containing material contains less than 20 wt. % water,        preferably less than 10 wt. % water,    -   b. contacting the cellulose-containing material with oxalic acid        dihydrate, and heating above the melting point of the oxalic        acid dihydrate, to obtain cellulose oxalates, wherein the dry        weight ratio between cellulose-containing material and oxalic        acid dihydrate is 1:1 to 1:100, preferably 1:1 to 1:50, more        preferably 1:1 to 1:10, most preferably 1:2.3 to 1.3.9,    -   c. washing the mixture resulting from step b),    -   d. preparing a suspension comprising the washed material from        step c), wherein the suspension is prepared using        micro-fluidization, and    -   e. recovering nanocellulose from the suspension,    -   wherein said nanocellulose is nanofibrillated cellulose.

In a fifth aspect of the invention there is provided a compositioncomprising nanofibrillated cellulose manufactured according to themethod disclosed in the fourth aspect of the invention.

In a sixth aspect of the invention there is provided a use of acomposition comprising nanofibrillated cellulose according to the fifthaspect of the invention in at least one of: automotive bio-basedcomposites such as fiberglass replacement for structural andnon-structural uses, cement additives, wet-strength additives,dry-strength additives, wet-end additives such as wet-end additives inpackaging coatings and films, transparent films for food packaging,polymer composite additives in composites, paper, electronic packaging,pharmaceutical excipients such as fillers, paper composites withsuperior strength properties, hygiene and absorbent products,mechanically enhanced spun fibers and textiles, cosmetic excipients suchas filler, food additives, insulation for buildings such as sound and/orheat barriers, aerospace composites, aerogels for oil and gas, pigmentssuch as architectural pigments, coatings, hydrophobic and self-cleaningcoatings, paints, dispersants, viscosity modulators, building materialssuch as structural composites, switchable optical devices, bonereplacement, tooth repair medical composites, strain sensors, filterssuch as filtration of water and air, flexible displays, OLED displays,flexible circuits, printable electronics, conductive substrates, solarpanels such as flexible solar panels, smart packaging, photonics, anddrug delivery.

In a seventh aspect there is provided a method for manufacturingnanocellulose intermediate, said method comprising the steps of:

-   -   a. providing a cellulose-containing material wherein the        cellulose-containing material contains less than 20 wt. % water,        preferably less than 10 wt. % water,    -   b. contacting the cellulose-containing material with oxalic acid        dihydrate, and heating above the melting point of the oxalic        acid dihydrate, to obtain cellulose oxalates,    -   c. washing the mixture resulting from step b),    -   wherein said nanocellulose intermediate is a nanocrystalline        cellulose intermediate.

In an eight aspect of the invention there is provided a compositioncomprising nanocrystalline cellulose intermediate manufactured accordingto the method disclosed in the seventh aspect of the invention.

In a ninth aspect of the invention there is provided a use of acomposition comprising nanocrystalline cellulose intermediate accordingto the eighth aspect of the invention in at least one of: automotivebio-based composites such as fiberglass replacement for structural andnon-structural uses, cement additives, wet-strength additives,dry-strength additives, wet-end additives such as wet-end additives inpackaging coatings and films, transparent films for food packaging,polymer composite additives in composites, paper, electronic packaging,pharmaceutical excipients such as fillers, paper composites withsuperior strength properties, hygiene and absorbent products,mechanically enhanced spun fibers and textiles, cosmetic excipients suchas filler, food additives, insulation for buildings such as sound and/orheat barriers, aerospace composites, aerogels for oil and gas, pigmentssuch as architectural pigments, coatings, hydrophobic and self-cleaningcoatings, paints, dispersants, viscosity modulators, building materialssuch as structural composites, switchable optical devices, bonereplacement, tooth repair medical composites, strain sensors, filterssuch as filtration of water and air, flexible displays, OLED displays,flexible circuits, printable electronics, conductive substrates, solarpanels such as flexible solar panels, smart packaging, photonics, anddrug delivery.

In a tenth aspect there is provided a method for manufacturingnanocellulose intermediate, said method comprising the steps of:

-   -   a. providing a cellulose-containing material wherein the        cellulose-containing material contains less than 20 wt. % water,        preferably less than 10 wt. % water,    -   b. contacting the cellulose-containing material with oxalic acid        dihydrate, and heating above the melting point of the oxalic        acid dihydrate, to obtain cellulose oxalates,    -   c. washing the mixture resulting from step b),    -   wherein said nanocellulose intermediate is a nanofibrillated        cellulose intermediate.

In an eleventh aspect of the invention there is provided a compositioncomprising nanofibrillated cellulose intermediate manufactured accordingto the method disclosed in the tenth aspect of the invention.

In a twelfth aspect of the invention there is provided a use of acomposition comprising nanofibrillated cellulose intermediate accordingto the eleventh aspect of the invention in at least one of: automotivebio-based composites such as fiberglass replacement for structural andnon-structural uses, cement additives, wet-strength additives,dry-strength additives, wet-end additives such as wet-end additives inpackaging coatings and films, transparent films for food packaging,polymer composite additives in composites, paper, electronic packaging,pharmaceutical excipients such as fillers, paper composites withsuperior strength properties, hygiene and absorbent products,mechanically enhanced spun fibers and textiles, cosmetic excipients suchas filler, food additives, insulation for buildings such as sound and/orheat barriers, aerospace composites, aerogels for oil and gas, pigmentssuch as architectural pigments, coatings, hydrophobic and self-cleaningcoatings, paints, dispersants, viscosity modulators, building materialssuch as structural composites, switchable optical devices, bonereplacement, tooth repair medical composites, strain sensors, filterssuch as filtration of water and air, flexible displays, OLED displays,flexible circuits, printable electronics, conductive substrates, solarpanels such as flexible solar panels, smart packaging, photonics, anddrug delivery.

Recovering nanocellulose in step e) in the above disclosed aspects ofthe invention is done by preparing a suspension of nanocellulose, amixture containing nanocellulose or a dry material containingnanocellulose. Thus, recovering nanocrystalline cellulose and/ornanofibrillated cellulose in step e) is done by preparing a suspensionof nanocrystalline cellulose and/or nanofibrillated cellulose, a mixturecontaining nanocrystalline cellulose and/or nanofibrillated cellulose,or a dry material containing nanocrystalline cellulose.

Further aspects and embodiments are defined in the appended claims,which are specifically incorporated herein by reference.

One advantage is that the cellulose oxalates were prepared with a quick,simple, direct and solvent-free treatment of pulp.

Another advantage is that a considerable amount of free carboxyl groupswere introduced while the macromolecular structure of cellulose wasbroken down to the nano-level due to hydrolysis.

A further advantage is that carboxyl functionalized nanocrystallinecellulose and/or nanofibrillated cellulose can be manufactured with highyields.

Compared to the conventional ways for the preparation of nanocrystallinecellulose and nanofibrillated cellulose, the present method is simplerwith much shorter procedures and more economic in terms of no use ofwater and expensive chemicals.

Yet another advantage is that it is possible to obtain nanocellulose athigh yield with a high concentration of carboxyl groups covalentlyattached.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is now described, by way of example, with reference to theaccompanying drawings, in which:

FIG. 1 shows a scheme of esterification of cellulose by oxalic aciddihydrate, as well as the most possible end product.

FIG. 2 shows FTIR (Fourier transform infrared spectroscopy) spectra ofsoftwood dissolving pulp (reference) and cellulose oxalates in examples1 to 4.

FIG. 3 shows CP/MAS ¹³C NMR (solid-state cross-polarization magic anglespinning carbon-13 NMR) spectrum of an example of cellulose oxalate.

FIGS. 4a and b are TEM (transmission electron microscopy) images ofnanocrystalline cellulose prepared from the cellulose oxalate in example3.

FIG. 5 is a FE-SEM (field-emission scanning electron microscopy) imageof nanocellulose containing both nanocrystalline and nanofibrillatedcellulose prepared from the cellulose oxalate in example 18.

FIG. 6 is an AFM (atomic force microscopy) image of nanocellulosecontaining both nanocrystalline and nanofibrillated cellulose preparedfrom the cellulose oxalate in example 18.

DETAILED DESCRIPTION

Before the invention is disclosed and described in detail, it is to beunderstood that this invention is not limited to particular compounds,configurations, method steps, substrates, and materials disclosed hereinas such compounds, configurations, method steps, substrates, andmaterials may vary somewhat. It is also to be understood that theterminology employed herein is used for the purpose of describingparticular embodiments only and is not intended to be limiting since thescope of the present invention is limited only by the appended claimsand equivalents thereof.

It must be noted that, as used in this specification and the appendedclaims, the singular forms “a”, “an” and “the” include plural referentsunless the context clearly dictates otherwise.

If nothing else is defined, any terms and scientific terminology usedherein are intended to have the meanings commonly understood by those ofskill in the art to which this invention pertains.

Nanocrystalline cellulose (NCC) as used throughout the description andthe claims denotes cellulose in crystalline form or at least inessentially or mostly crystalline form, since less-ordered forms alsoexist in most NCCs. NCCs are rigid rod-like crystals with diameter inthe range of 5-40 nm and lengths of typically a few hundred nanometers,in the range of 100-600 nm. (Osong S. H., Norgren S. and Engstrand P.2016. Processing of wood-based microfibrillated cellulose andnanofibrillated cellulose, and applications relating to papermaking: areview. Cellulose 23: 93-123)

Nanofibrillated cellulose (NFC) or microfibrillated cellulose (MFC) asused throughout the description and the claims denotes cellulosecontaining both crystalline and less-ordered forms. NFCs or MFCs havediameters in the range of 5-100 nm and lengths of >600 nm to several μm.(Osong S. H., Norgren S. and Engstrand P. 2015. Processing of wood-basedmicrofibrillated cellulose and nanofibrillated cellulose, andapplications relating to papermaking: a review. Cellulose 23: 93-123;Nelson K., Retsina T., Iakovlev M., van Heiningen A., Deng Y., ShatkinJ. A. and Mulyadi. 2016. Chapter 9. American Process: production of lowcost nanocellulose for renewable, advanced materials applications. InMaterials Research for Manufacturing. Eds. Madsen L. D. and Svedberg E.B. Springer International Publishing, Switzerland. pp. 267-302)

Cellulose-containing material is material comprising cellulose. Examplesinclude but are not limited to wood pulp, non-wood pulp, cotton, andbacterial cellulose. It encompasses wood pulps as well as commercialmicrocrystalline cellulose produced from cotton linter.

Oxalic acid dihydrate (OAD) has a relatively low melting point of104-106° C., which makes it possible to mix the molten OAD with pulp(cellulose-containing material) to carry out the esterification ofcellulose.

A nanocellulose intermediate is a precursor of nanocellulose. Ananocrystalline cellulose intermediate is a precursor of nanocrystallinecellulose. A nanofibrillated cellulose intermediate is a precursor ofnanofibrillated cellulose. The nanocellulose, nanocrystalline celluloseand nanofibrillated cellulose intermediates are produced in step c),i.e. when washing the mixture resulting from step b).

In a first aspect there is provided a method for manufacturingnanocellulose, said method comprising the steps of:

-   a) providing a cellulose-containing material wherein the    cellulose-containing material contains less than 20 wt. % water,    preferably less than 10 wt. % water,-   b) contacting the cellulose-containing material with oxalic acid    dihydrate, and heating above the melting point of the oxalic acid    dihydrate, to obtain cellulose oxalates,-   c) washing the mixture resulting from step b),-   d) preparing a suspension comprising the washed material from step    c), and-   e) recovering nanocrystalline cellulose from the suspension,-   wherein said nanocellulose is nanocrystalline cellulose.

In one embodiment the dry weight ratio between cellulose-containingmaterial and oxalic acid dihydrate is 1:1 to 1:100, preferably 1:1 to1:50, more preferably 1:1 to 1:10, most preferably 1:2.3 to 1:3.9.

In one embodiment oxalic acid dihydrate has a purity of 95-100 wt. %,preferably ≥99 wt. %.

In one embodiment the reaction in step b) is solvent-free.

In one embodiment the cellulose-containing material provided in step a)comprises at least 80 wt. % cellulose, preferably at least 90 wt. %. Inone embodiment the cellulose-containing material provided in step a) isbleached.

In one embodiment the cellulose-containing material and the oxalic aciddihydrate are heated above 106° C., preferably above 110° C. in step b).In one embodiment the cellulose-containing material and the oxalic aciddihydrate are heated to a temperature in the interval 104-106° C.(approximate melting point of oxalic acid dihydrate), in otherembodiments other intervals for the temperature are used including105-107° C., 104-108° C., 105-110° C., 105-111° C., 104-111° C., and104-112° C. In one embodiment the temperature in step b) does not exceed120° C. The temperature should not be too high, otherwise the materialwill become dark during the reaction with oxalic acid dihydrate. Thematerial becomes less useful when it becomes dark. Darkening can bothoccur at too high temperatures, typically above 120° C. and duringextended treatment times, typically in excess of 120 minutes.

In one embodiment the cellulose-containing material and the oxalic aciddihydrate are mixed during step b). In one embodiment step b) is carriedout in an extruder, a thermostatic reaction vessel, or a sealed pressurevessel.

In one embodiment the cellulose-containing material and the oxalic aciddihydrate are heated above the melting point of the oxalic aciddihydrate for a time in the interval 5-120 minutes, preferably 30-60minutes.

In one embodiment the mixture is washed in step c) with at least oneselected from the group consisting of ethanol, acetone, water, and THF.In an alternative embodiment the mixture is washed in step c) with atleast one selected from the group consisting of water, ethanol, acetone,THF, and ethyl acetate. In yet another embodiment the mixture is washedin step c) with at least one solvent which is capable of dissolvingoxalic acid dihydrate.

In one embodiment the washed material from step c) is mixed with waterto obtain a suspension. As desired the pH and ionic strength of thesuspension can be adjusted.

In one embodiment the suspension is prepared at a pH in the interval9-10 in step d).

In one embodiment the suspension is prepared using at least one selectedfrom the group consisting of sonication, micro-fluidization, andmechanical disintegration. It has been found that the use of sonicationand micro-fluidization increase the yield of the process.

In one embodiment nanocrystalline cellulose in step e) is recovered fromthe suspension after centrifugation. The suspension is centrifuged andthe nanocrystalline cellulose will remain in suspension whereas otherparts will sediment.

In a second aspect of the invention a composition comprisingnanocrystalline cellulose is manufactured according to the methoddisclosed in the first aspect and embodiments thereof.

In one embodiment the composition comprising nanocrystalline cellulosecomprises nanocrystalline cellulose having free carboxyl groups.

In one embodiment the composition comprising nanocrystalline cellulosecomprises free carboxyl groups with a density in the range 0.2-1.3mmol/g, preferably 0.4-1.3 mmol/g. It is an advantage of the processthat a high density of carboxyl groups can be obtained. Also carboxylgroup-density in the ranges 0.5-1.3, 0.6-1.3, 0-7-1.3, 0.8-1.3, 0.9-1.3,1.0-1.3, or 1.1-1.3 mmol/g are envisaged. In one embodiment the carboxylgroups are part of oxalate residues.

In one embodiment the composition comprising nanocrystalline cellulosefurther comprises nanofibrillated cellulose.

In one embodiment the composition comprising nanocrystalline cellulosefurther comprises nanofibrillated cellulose having free carboxyl groups.

In one embodiment the composition comprising nanocrystalline cellulosefurther comprises nanofibrillated cellulose having free carboxyl groupswith a density in the range 0.2-1.3 mmol/g, preferably 0.4-1.3 mmol/g.It is an advantage of the process that a high density of carboxyl groupscan be obtained. Also carboxyl group-density in the ranges 0.5-1.3,0.6-1.3, 0-7-1.3, 0.8-1.3, 0.9-1.3, 1.0-1.3, or 1.1-1.3 mmol/g areenvisaged. In one embodiment the carboxyl groups are part of oxalateresidues.

In a third aspect of the invention the composition comprisingnanocrystalline cellulose of the second aspect of the invention is usedin at least one: automotive bio-based composites such as fiberglassreplacement for structural and non-structural uses, cement additives,wet-strength additives, dry-strength additives, wet-end additives suchas wet-end additives in packaging coatings and films, transparent filmsfor food packaging, polymer composite additives in composites, paper,electronic packaging, pharmaceutical excipients such as fillers, papercomposites with superior strength properties, hygiene and absorbentproducts, mechanically enhanced spun fibers and textiles, cosmeticexcipients such as filler, food additives, insulation for buildings suchas sound and/or heat barriers, aerospace composites, aerogels for oiland gas, pigments such as architectural pigments, coatings, hydrophobicand self-cleaning coatings, paints, dispersants, viscosity modulators,building materials such as structural composites, switchable opticaldevices, bone replacement, tooth repair medical composites, strainsensors, filters such as filtration of water and air, flexible displays,OLED displays, flexible circuits, printable electronics, conductivesubstrates, solar panels such as flexible solar panels, smart packaging,photonics, and drug delivery.

In a fourth aspect there is provided a method for manufacturingnanocellulose, said method comprising the steps of:

-   -   a) providing a cellulose-containing material wherein the        cellulose-containing material contains less than 20 wt. % water,        preferably less than 10 wt. % water,    -   b) contacting the cellulose-containing material with oxalic acid        dihydrate, and heating above the melting point of the oxalic        acid dihydrate, to obtain cellulose oxalates, wherein the dry        weight ratio between cellulose-containing material and oxalic        acid dihydrate is 1:1 to 1:100, preferably 1:1 to 1:50, more        preferably 1:1 to 1:10, most preferably 1:2.3 to 1.3.9,    -   c) washing the mixture resulting from step b),    -   d) preparing a suspension comprising the washed material from        step c), wherein the suspension is prepared using        micro-fluidization, and    -   e) recovering nanocellulose from the suspension,

-   wherein said nanocellulose is nanofibrillated cellulose.

In one embodiment the cellulose-containing material provided in step a)comprises at least 80 wt. % cellulose, preferably at least 90 wt. %.

In one embodiment the cellulose-containing material provided in step a)is bleached.

In one embodiment oxalic acid dihydrate has a purity of 95-100 wt. %,preferably 99 wt. %.

In one embodiment the reaction in step b) is solvent-free.

In one embodiment oxalic acid dihydrate has a purity of 95-100 wt. %,preferably 99 wt. %.

In one embodiment the cellulose-containing material and the oxalic aciddihydrate are heated above 106° C., in step b).

In one embodiment the cellulose-containing material and the oxalic aciddihydrate are heated above 110° C., in step b).

In one embodiment the temperature in step b) does not exceed 120° C.

In one embodiment the cellulose-containing material and the oxalic aciddihydrate are mixed during step b).

In one embodiment step b) is carried out in an extruder, or athermostatic reaction vessel, or a sealed pressure vessel.

In one embodiment the cellulose-containing material and the oxalic aciddihydrate are heated above the melting point of the oxalic aciddihydrate for a time in the interval 5-120 minutes, preferably 30-60minutes.

In one embodiment the mixture is washed in step c) with at least onesolvent capable of dissolving oxalic acid dihydrate.

In one embodiment the mixture is washed in step c) with at least oneselected from the group consisting of ethanol, acetone, water, and THF.

In one embodiment washed material from step c) is mixed with water toobtain a suspension.

In one embodiment the suspension is prepared at a pH in the interval9-10 in step d).

In one embodiment nanofibrillated cellulose in step e) is recovered fromthe suspension after centrifugation.

In one embodiment cellulose-containing material is not contacted with adeep eutectic solvent(s).

In a fifth aspect of the invention a composition comprisingnanofibrillated cellulose is manufactured according to the methoddisclosed in the fourth aspect and embodiments thereof.

In one embodiment the composition comprising nanofibrillated cellulosecomprises nanofibrillated cellulose having free carboxyl groups.

In one embodiment the composition comprising nanofibrillated cellulosecomprises nanofibrillated cellulose having free carboxyl groups with adensity in the range 0.2-1.3 mmol/g, preferably 0.4-1.3 mmol/g. It is anadvantage of the process that a high density of carboxyl groups can beobtained. Also carboxyl group-density in the ranges 0.5-1.3, 0.6-1.3,0-7-1.3, 0.8-1.3, 0.9-1.3, 1.0-1.3, or 1.1-1.3 mmol/g are envisaged. Inone embodiment the free carboxyl groups are part of oxalate residues.

In a sixth aspect of the invention the composition comprisingnanofibrillated cellulose according to fifth aspect of the invention isused at least in one of: automotive bio-based composites such asfiberglass replacement for structural and non-structural uses, cementadditives, wet-strength additives, dry-strength additives, wet-endadditives such as wet-end additives in packaging coatings and films,transparent films for food packaging, polymer composite additives incomposites, paper, electronic packaging, pharmaceutical excipients suchas fillers, paper composites with superior strength properties, hygieneand absorbent products, mechanically enhanced spun fibers and textiles,cosmetic excipients such as filler, food additives, insulation forbuildings such as sound and/or heat barriers, aerospace composites,aerogels for oil and gas, pigments such as architectural pigments,coatings, hydrophobic and self-cleaning coatings, paints, dispersants,viscosity modulators, building materials such as structural composites,switchable optical devices, bone replacement, tooth repair medicalcomposites, strain sensors, filters such as filtration of water and air,flexible displays, OLED displays, flexible circuits, printableelectronics, conductive substrates, solar panels such as flexible solarpanels, smart packaging, photonics, and drug delivery.

In a seventh aspect there is provided a method for manufacturingnanocellulose intermediate, said method comprising the steps of:

-   -   a. providing a cellulose-containing material wherein the        cellulose-containing material contains less than 20 wt. % water,        preferably less than 10 wt. % water,    -   b. contacting the cellulose-containing material with oxalic acid        dihydrate, and heating above the melting point of the oxalic        acid dihydrate, to obtain cellulose oxalates,    -   c. washing the mixture resulting from step b),    -   wherein said nanocellulose intermediate is a nanocrystalline        cellulose intermediate.

In one embodiment the cellulose-containing material provided in step a)comprises at least 80 wt. % cellulose, preferably at least 90 wt. %.

In one embodiment the cellulose-containing material provided in step a)is bleached.

In one embodiment the dry weight ratio between cellulose-containingmaterial and oxalic acid dihydrate is 1:1 to 1:100, preferably 1:1 to1:50, more preferably 1:1 to 1:10, most preferably 1:2.3 to 1:3.9.

In one embodiment oxalic acid dihydrate has a purity of 95-100 wt. %,preferably ≥99 wt. %.

In one embodiment the reaction in step b) is solvent-free.

In one embodiment the cellulose-containing material and the oxalic aciddihydrate are heated above 106° C., in step b).

In one embodiment the cellulose-containing material and the oxalic aciddihydrate are heated above 110° C., in step b).

In one embodiment the temperature in step b) does not exceed 120° C.

In one embodiment the cellulose-containing material and the oxalic aciddihydrate are mixed during step b).

In one embodiment step b) is carried out in an extruder, or athermostatic reaction vessel, or a sealed pressure vessel.

In one embodiment the cellulose-containing material and the oxalic aciddihydrate are heated above the melting point of the oxalic aciddihydrate for a time in the interval 5-120 minutes, preferably 30-60minutes.

In one embodiment the mixture is washed in step c) with at least onesolvent capable of dissolving oxalic acid dihydrate.

In one embodiment the mixture is washed in step c) with at least oneselected from the group consisting of ethanol, acetone, water, and THF.

In an eighth aspect of the invention there is provided a compositioncomprising nanocrystalline cellulose intermediate manufactured accordingto the eighth aspect of the invention.

In one embodiment the composition comprising nanocrystalline celluloseintermediate comprises nanocrystalline cellulose intermediate havingfree carboxyl groups.

In one embodiment the composition comprising nanocrystalline celluloseintermediate comprises nanocrystalline cellulose intermediate havingfree carboxyl groups with a density in the range 0.2-1.3 mmol/g,preferably 0.4-1.3 mmol/g. Also carboxyl group-density in the ranges0.5-1.3, 0.6-1.3, 0-7-1.3, 0.8-1.3, 0.9-1.3, 1.0-1.3, or 1.1-1.3 mmol/gare envisaged. In one embodiment the free carboxyl groups are part ofoxalate residues.

In one embodiment the composition comprising nanocrystalline celluloseintermediate further comprises nanofibrillated cellulose intermediate.

In one embodiment the composition comprising nanocrystalline celluloseintermediate comprises nanofibrillated cellulose intermediate havingfree carboxyl groups.

In one embodiment the composition comprising nanocrystalline celluloseintermediate comprises nanofibrillated cellulose intermediate havingfree carboxyl groups with a density in the range 0.2-1.3 mmol/g,preferably 0.4-1.3 mmol/g. Also carboxyl group-density in the ranges0.5-1.3, 0.6-1.3, 0-7-1.3, 0.8-1.3, 0.9-1.3, 1.0-1.3, or 1.1-1.3 mmol/gare envisaged. In one embodiment the free carboxyl groups are part ofoxalate residues.

In a ninth aspect of the invention the composition comprisingnanocrystalline cellulose intermediate according to the eight aspect ofthe invention is used at least in one of: automotive bio-basedcomposites such as fiberglass replacement for structural andnon-structural uses, cement additives, wet-strength additives,dry-strength additives, wet-end additives such as wet-end additives inpackaging coatings and films, transparent films for food packaging,polymer composite additives in composites, paper, electronic packaging,pharmaceutical excipients such as fillers, paper composites withsuperior strength properties, hygiene and absorbent products,mechanically enhanced spun fibers and textiles, cosmetic excipients suchas filler, food additives, insulation for buildings such as sound and/orheat barriers, aerospace composites, aerogels for oil and gas, pigmentssuch as architectural pigments, coatings, hydrophobic and self-cleaningcoatings, paints, dispersants, viscosity modulators, building materialssuch as structural composites, switchable optical devices, bonereplacement, tooth repair medical composites, strain sensors, filterssuch as filtration of water and air, flexible displays, OLED displays,flexible circuits, printable electronics, conductive substrates, solarpanels such as flexible solar panels, smart packaging, photonics, anddrug delivery.

In a tenth aspect of the invention there is provided a method formanufacturing nanocellulose intermediate, said method comprising thesteps of:

-   -   a. providing a cellulose-containing material wherein the        cellulose-containing material contains less than 20 wt. % water,        preferably less than 10 wt. % water,    -   b. contacting the cellulose-containing material with oxalic acid        dihydrate, and heating above the melting point of the oxalic        acid dihydrate, to obtain cellulose oxalates, wherein the dry        weight ratio between cellulose-containing material and oxalic        acid dihydrate is 1:1 to 1:100, preferably 1:1 to 1:50, more        preferably 1:1 to 1:10, most preferably 1:2.3 to 1.3.9,    -   c. washing the mixture resulting from step b),    -   wherein said nanocellulose intermediate is nanofibrillated        cellulose intermediate.

In one embodiment the cellulose-containing material provided in step a)comprises at least 80 wt. % cellulose, preferably at least 90 wt. %.

In one embodiment the cellulose-containing material provided in step a)is bleached.

In one embodiment oxalic acid dihydrate has a purity of 95-100 wt. %,preferably 99 wt. %.

In one embodiment the reaction in step b) is solvent-free.

In one embodiment the cellulose-containing material and the oxalic aciddihydrate are heated above 106° C., in step b).

In one embodiment the cellulose-containing material and the oxalic aciddihydrate are heated above 110° C., in step b).

In one embodiment the temperature in step b) does not exceed 120° C.

In one embodiment the cellulose-containing material and the oxalic aciddihydrate are mixed during step b).

In one embodiment step b) is carried out in an extruder, or athermostatic reaction vessel, or a sealed pressure vessel.

In one embodiment the cellulose-containing material and the oxalic aciddihydrate are heated above the melting point of the oxalic aciddihydrate for a time in the interval 5-120 minutes, preferably 30-60minutes.

In one embodiment the mixture is washed in step c) with at least onesolvent capable of dissolving oxalic acid dihydrate.

In one embodiment the mixture is washed in step c) with at least oneselected from the group consisting of ethanol, acetone, water, and THF.

In one embodiment washed material from step c) is mixed with water toobtain a suspension.

In one embodiment cellulose-containing material is not contacted with adeep eutectic solvent(s).

In an eleventh aspect of the invention there is provided a compositioncomprising nanofibrillated cellulose intermediate manufactured accordingto the tenth aspect of the invention.

In one embodiment the composition comprising nanofibrillated celluloseintermediate comprises nanofibrillated cellulose intermediate havingfree carboxyl groups.

In one embodiment the composition comprising nanofibrillated celluloseintermediate comprises nanofibrillated cellulose intermediate havingfree carboxyl groups with a density in the range 0.2-1.3 mmol/g,preferably 0.4-1.3 mmol/g. Also carboxyl group-density in the ranges0.5-1.3, 0.6-1.3, 0-7-1.3, 0.8-1.3, 0.9-1.3, 1.0-1.3, or 1.1-1.3 mmol/gare envisaged. In one embodiment the free carboxyl groups are part ofoxalate residues.

In a twelfth aspect of the invention there is provided a compositioncomprising nanofibrillated cellulose intermediate used in least one of:automotive bio-based composites such as fiberglass replacement forstructural and non-structural uses, cement additives, wet-strengthadditives, dry-strength additives, wet-end additives such as wet-endadditives in packaging coatings and films, transparent films for foodpackaging, polymer composite additives in composites, paper, electronicpackaging, pharmaceutical excipients such as fillers, paper compositeswith superior strength properties, hygiene and absorbent products,mechanically enhanced spun fibers and textiles, cosmetic excipients suchas filler, food additives, insulation for buildings such as sound and/orheat barriers, aerospace composites, aerogels for oil and gas, pigmentssuch as architectural pigments, coatings, hydrophobic and self-cleaningcoatings, paints, dispersants, viscosity modulators, building materialssuch as structural composites, switchable optical devices, bonereplacement, tooth repair medical composites, strain sensors, filterssuch as filtration of water and air, flexible displays, OLED displays,flexible circuits, printable electronics, conductive substrates, solarpanels such as flexible solar panels, smart packaging, photonics, anddrug delivery.

Recovering nanocellulose in step e) in the above disclosed aspects andembodiments is done by preparing a suspension of nanocellulose, amixture containing nanocellulose or a dry material containingnanocellulose. Thus, recovering nanocrystalline cellulose and/ornanofibrillated cellulose in step e) is done by preparing a suspensionof nanocrystalline cellulose and/or nanofibrillated cellulose, a mixturecontaining nanocrystalline cellulose and/or nanofibrillated cellulose,or a dry material containing nanocrystalline cellulose and/ornanofibrillated cellulose.

All the described alternative embodiments above or parts of anembodiment can be freely combined without departing from the inventiveidea as long as the combination is not contradictory.

Other features and uses of the invention and their associated advantageswill be evident to a person skilled in the art upon reading thedescription and the examples.

It is to be understood that this invention is not limited to theparticular embodiments shown here. The embodiments are provided forillustrative purposes and are not intended to limit the scope of theinvention since the scope of the present invention is limited only bythe appended claims and equivalents thereof.

EXPERIMENTAL

All percentages and ratios are calculated by weight unless clearlyindicated otherwise.

Materials. Commercially available softwood dissolving pulp (cellulosecontent 96%), hardwood dissolving pulp (cellulose content 97%),microcrystalline cellulose (Avicel PH-101, cellulose content 100%), andbleached softwood kraft pulp (cellulose content>80%) were used ascellulose raw material. Each dried pulp was manually torn to smallerpieces (around 2×2 cm²). Oxalic acid dihydrate (≥99%), tetrahydrofuran(THF, ≥99.99%), acetone (≥99%), and ethanol (≥95%) were commerciallyavailable. Deionized water was used to prepare all suspensions of theresulting nanocrystalline celluloses.

Esterification of cellulose by oxalic acid dihydrate. Each pulp wasmixed with oxalic acid dihydrate according to the dry weight ratios of1/2.3 or 1/3.9. Each mixture was heated at 110° C. for 30 min, 35 min,or 60 min under constant mixing, to obtain cellulose oxalates (see allexamples in Tables 1 and 2). After the reaction, each mixture was washedby THF, ethanol, or acetone to remove the excess oxalic acid dihydrateand then Soxhlet extracted by THF or ethanol for 20 h, or washedexcessively by filtration of ethanol or acetone until the conductivityof filtrate was below 2 μS cm⁻¹. Then all samples were dried either infume hood or at 50° C. in an oven.

Preparation of nanocrystalline cellulose suspension. Aqueous suspensionsof cellulose oxalates with pH 9-10 were prepared. Each suspension wassonicated with 40% amplitude and centrifuged. The supernatant wascollected to obtain a suspension of nanocrystalline cellulose.

Some of the aqueous suspensions of cellulose oxalates with pH 9-10 werehomogenized in a micro-fluidizer with 1 pass at 925 bar through a 400 μmand a 200 μm chamber, and then with 1 to 5 passes at 1600 bar through a200 μm and a 100 μm chamber, to obtain gel-like suspensions ofnanocrystalline cellulose with a consistency of 1.5 wt. %. Some of suchsuspensions were diluted 6 times and centrifuged. The supernatant wascollected and dried at 105° C. in an oven, to calculate the yield ofnanocrystalline cellulose that was stably dispersed in water.

According to our tests, using micro-fluidization can convert nearly 100%of the nanocellulose intermediate to nanocellulose if water is used asthe liquid media. Moreover, our tests, no matter what types of media areused (i.e. water, organic solvent(s), a mixture of both water andorganic solvent(s), oil(s), emulsion(s), paint(s), adhesive(s) etc.),the suspensions after micro-fluidization (or any manners of high-sheardisintegration) always contain nanocellulose.

Results

The total carboxyl content (TCC) of cellulose oxalates in examples 1 to4, as determined by alkaline hydrolysis and back titration(Peydecastaing J., Vaca-Garcia C. and Borredon E. 2009. Accuratedetermination of the degree of substitution of long chain celluloseesters. Cellulose 16: 289-297.), showed the amounts of carboxyl groupsfrom both carboxylic acids (—COOH) and esters (—COO—) of the celluloseoxalates. The values of TCC showed the same trend as that of the degreeof substitution (DS), where the highest DS of 0.30 and TCC of 1.63mmol/g were given by the cellulose oxalate in example 3 (Table 3). Forcomparison, the conductometric titration method was applied. This methodonly determines the free carboxyl content (FCC). The free carboxylgroups were in the forms of acids. The highest FCC of 1.30 mmol/g wasgiven by the cellulose oxalates in examples 3 and 4.

The appearance of cellulose changed significantly due to theesterification. The original pulp sheet pieces turned into very finepowders, which indicated the breakdown of the macromolecular structurearising from, probably, the acid hydrolysis. To verify the assumption,the molecular weight (Mw) properties of cellulose oxalates weredetermined by size exclusion chromatography.

The treatment of cellulose with oxalic acid dihydrate caused asubstantial decrease of Mw, as shown by Table 1. The Mws of thecellulose oxalates in examples 1 to 4 were around 40 kDa, which wereonly one tenth of the Mw of the corresponding raw material (softwooddissolving pulp). Cellulose underwent a quick and severe acid hydrolysisduring the esterification might be the reason.

Some pulps became dark brown or black after the reaction. The restsremained white or became slightly grey, and the gravimetric yields ofthese samples were 82-99% (Tables 1 and 2). Therefore, only thesesamples were analyzed and used to prepare aqueous suspensions for thefollowing sonication or micro-fluidization.

Free carboxyl groups were introduced on cellulose through theesterification, and their contents were 0.2-1.3 mmol/g (Tables 1 and 2).The values of anionic charge density are higher than that of thesulfuric acid-treated cellulose, which was 0.17 mmol/g (Ureña-benavidesE. E., Ao G., Davis V. A., Kitchens, C. L. 2011. Rheology and phasebehavior of lyotropic cellulose nanocrystal suspensions. Macromolecules44:8990-8998.).

Amongst other chemical derivatization routes the free carboxylic acidfunctional groups can be used for further derivatization, such aspreparing acyl chlorides by reacting with thionyl chloride SOCl₂,preparing acid anhydrides by reacting with carboxylic acids, preparingesters by reacting with alcohols, preparing thioesters by reacting withthiols, preparing amides by reacting with amines, and preparing alcoholsby reduction. The cellulose-oxalate esters can be hydrolyzed to produceuncharged cellulose again. At alkaline conditions, the carboxylic acidgroups can be converted to carboxylate groups, which can adsorb cationicquaternary ammonium salts having alkyl, phenyl, glycidyl, and diallylgroups through electrostatic attraction, to prepare hydrophobicnanocellulose (Salajkova M, Berglund L A, Zhou Q. 2012 Hydrophobiccellulose nanocrystals modified with quaternary ammonium salts. J.Mater. Chem. 22:19798-19805.).

It is noteworthy that the cellulose oxalates washed and Soxhletextracted by ethanol had lower FCCs than the ones washed by THF,probably due to the esterification or alcoholysis that happened betweenethanol and the free carboxyl groups.

The onset temperature of thermal degradation of the cellulose oxalateswere 173-177° C. (Table 2), which can be correlated to the modified andless-ordered surfaces of cellulose. Considering the onset temperatures,the cellulose oxalates and probably the resulting nanocellulose can beused as reinforcing fillers for thermoplastics, such as polystyrene (PS,melting temperature 74-105° C.), acrylonitrile-butadine-styrenecopolymers (ABS, melting temperature 88-125° C.), low densitypolyethylene (LDPE, melting temperature 103-110° C.), linear low densitypolyethylene (LLDPE, melting temperature 110-125° C.), high densitypolyethylene (HDPE melting temperature 125-132° C.), polycarbonate (PC,melting temperature 145° C.), and polypropylene (PP, melting temperature150-175° C.) (Dolinar B. 2005. Improved variegated composites andrelated methods of manufacture. WO 2005123364 A1.).

The solvent used to wash the cellulose oxalates could be evaporated torecover the excess oxalic acid dihydrate, which could be thenrecrystallized in ethyl acetate to obtain pure oxalic acid dihydrate.

Preparation and characterization of nanocellulose.

The samples that were homogenized formed a thick gel at a consistency of1.5 wt. %. The samples that were prepared through sonication had a lessviscous appearance.

The supernatants collected after centrifugation were somewhat turbid ortransparent.

Transmission electron microscopy images shown in FIGS. 4a and bconfirmed the presence of nanocrystalline cellulose in the preparedsuspension. The shape of nanostructured cellulose appeared to beindividual rods with widths in the range of 16-20 nm and lengths in therange of 150-220 nm. A field-emission scanning electron microscopy imageshown in FIG. 5, and an atomic force microscopy image shown in FIG. 6confirmed the presence of nanocrystalline and nanofibrillated cellulosein the prepared suspension. The shape of nanostructured celluloseappeared to be individual rods as well as short fibrils, with width inthe range of 15-36 nm and lengths in the range of 260-900 nm. When theconcentrated suspension was observed between the crossed polarizers,birefringence patterns were shown. Moreover, it was possible to preparetransparent films through solvent-casting of the nanocellulosesuspension. The films exhibited iridescent color while tilted underlight. By X-ray diffraction, the crystallinity indexes of the films inall examples were 68%-80%, which confirmed that the preparednanocelluloses were mostly crystalline (Table 1). It was also possibleto prepare transparent films by membrane filtration followed bysuspended drying at 93° C. under vacuum. The films exhibited goodtensile properties. Films made from example 20 had a tensile strength of136.6±8.7 MPa, an elongation at break of 3.0±0.6%, and an elasticmodulus of 10.6±0.6 GPa. Films made from example 22 had a tensilestrength of 195.3±9.9 MPa, an elongation at break of 5.0±0.9%, and anelastic modulus of 10.2±0.5 GPa. By X-ray diffraction, the crystallinityindexes of the films made from examples 20 and 22 were 76% and 67%,respectively (Table 2).

By dynamic light scattering, the z-average sizes of the nanoparticles inall examples were 109-535 nm with narrow distributions. The gravimetricyields of nanocrystalline celluloses were 42-94%, as calculated from thedry weight of raw materials (Tables 1 and 2).

The described method can be used to prepare pure nanocrystallinecellulose as evident by the size and crystallinity indexes of thematerials (Tables 1 and 2). When preparing nanocellulose by using amicro-fluidizer the material consisted of a mixture of bothnanocrystalline and nanofibrillated cellulose, as evident by themicrographs and the size of the particles. A longer aspect ratio wasalso indicated by the gelation tendencies. It is possible to preparepure nanofibrillated cellulose by preparing the material in a reactorwhere the reaction time, pulp particle size and mixing has beenoptimized to give milder and more homogeneous conditions.

TABLE 1 Summary of examples of esterification of cellulose by oxalicacid dihydrate, preparation of nanocrystalline cellulose (NCC) bysonication, and characterizations of cellulose oxalates and theresulting NCC. Sonication Total Esterification gravimetricCharacterization Weight Gravi- yield (%) Free Molecular ratio metric ofNCC carboxyl weight Crystall- Poly- of pulp/ Washing^(b) yield (%) aftercontent^(c) (kDa) inity z- dispersity oxalic Reaction agent aftersonication (nmol/g) of of index average index Type of raw acid timeafter esterifi- and cellulose cellulose (%) of (nm) of of Examplematerial dihydrate (min) reaction cation centrifuge oxalate oxalate NCCNCC NCC 1 Softwood 1/3.9 15 THF NA^(a) NA^(a) 1.22 38 NA^(a) NA^(a)NA^(a) dissolving pulp 2 Softwood 1/3.9 30 THF 99 58 1.26 44 68.2 1700.41 dissolving pulp 3 Softwood 1/3.9 60 THF 94 61 1.30 44 75.5 159 0.57dissolving pulp 4 Softwood 1/3.9 120 THF NA^(a) NA^(a) 1.30 41 NA^(a)NA^(a) NA^(a) dissolving pulp 5 Softwood 1/3.9 30 Ethanol 93 55 0.39NA^(a) 69.6 182 0.44 dissolving pulp 6 Softwood 1/3.9 60 Ethanol 68 620.29 NA^(a) 75.3 180 0.46 dissolving pulp 7 Ground 1/2.3 30 Ethanol 8955 0.30 NA^(a) 80.3 395 0.52 (20 mesh) softwood dissolving pulp 8 Ground1/2.3 60 Ethanol 82 64 0.31 NA^(a) 79 051 3.31 (20 mesh) softwooddissolving pulp 9 Softwood 1/2.3 30 Ethanol 97 42 0.15 NA^(a) 74.4 5170.49 dissolving pulp 10 Softwood 1/2.3 60 Ethanol 94 56 0.18 NA^(a) 75.5535 0.52 dissolving pulp 11 Hardwood 1/2.3 30 Ethanol 92 51 0.18 NA^(a)73.4 394 0.51 dissolving pulp 12 Hardwood 1/2.3 60 Ethanol 84 63 0.18NA^(a) 73.3 260 0.55 dissolving pulp 13 Avicel PH-101 1/2.3 30 Ethanol93 65 0.18 NA^(a) 78.8 452 0.47 (microcrystalline cellulose) 14 AvicelPH-101 1/2.3 60 Ethanol 89 57 0.22 NA^(a) 79.8 359 0.50(microcrystalline cellulose) 15 Freeze-dried 1/2.3 30 Ethanol 91 51 0.10NA^(a) 72.4 391 0.79 bleached softwood kraft pulp ^(a)NA: not available.^(b)Washing by Soxhlet extraction. ^(c)Determined by conductometrictitration.

TABLE 2 Summary of examples of esterification of cellulose by oxalicacid dihydrate, preparation of nanocellulose (NC) by micro-fluidization,and characterizations of cellulose oxalates and the resulting NC.Microfluid- ization Characterization Total Onset Esterificationgravimetric temperature Gravi- yield (%) of Weight metric of NC Freethermal ratio yield after carboxyl degradation Crystall- Poly- of pulp/Washing^(b) (%) microfluid- content^(c) of inity z- dispersity Type ofoxalic Reaction agent after ization (nmol/g) of cellulose index averageindex raw acid time after esterifi- and cellulose oxalate (%) of (nm) ofof Example material dihydrate (min) reaction cation centrifuge oxalate(° C.) NC NC NC 16 Softwood 1/3.9 60 Ethanol 85 NA^(a) 0.62 175 NA^(a)NA^(a) NA^(a) dissolving pulp 17 Softwood 1/3.9 60 Ethanol 86 NA^(a)0.97 176 NA^(a) NA^(a) NA^(a) kraft pulp 18 Softwood 1/3.9 35 Ethanol 84NA^(a) 0.92 177 NA^(a) NA^(a) NA^(a) kraft pulp 19 Softwood 1/3.9dissolving 35 Ethanol 94 NA^(a) 0.86 175 NA^(a) NA^(a) NA^(a) pulp 20Softwood 1/3.9 35 Acetone 97 90 1.05 176 75.4 183 0.49 dissolving pulp21 Softwood 1/3.9 60 Acetone 96 NA^(a) 1.08 175 NA^(a) NA^(a) NA^(a)dissolving pulp 22 Softwood 1/3.9 35 Acetone 96 94 1.10 173 65.5 1090.37 kraft pulp 23 Softwood 1/3.9 60 Acetone 99 NA^(a) 1.04 NNA^(a)NA^(a) NA^(a) NA^(a) kraft pulp ^(a)NA: not available. ^(b)Washing byfiltration of ethanol or acetone until the conductivity of filtrate wasbelow 2 μS cm⁻¹. ^(c)Determined by conductometric titration.

TABLE 3 Degree of substitution and total carboxyl content of thecellulose oxalates in examples 1 to 4, as determined by alkalinehydrolysis and back titration. Total carboxyl Reaction Degree content(mmol/g) time of of cellulose Example (min) substitution oxalate 1  150.23 1.30 2  30 0.29 1.57 3  60 0.30 1.63 4 120 0.28 1.53

1. A method for manufacturing nanocellulose, said method comprising thesteps of: a. providing a cellulose-containing material wherein thecellulose-containing material contains less than 20 wt. % water,preferably less than 10 wt. % water, b. contacting thecellulose-containing material with oxalic acid dihydrate, and heatingabove the melting point of the oxalic acid dihydrate, to obtaincellulose oxalates, c. washing the mixture resulting from step b), d.preparing a suspension comprising the washed material from step c), ande. recovering nanocellulose from the suspension, wherein saidnanocellulose is nanocrystalline cellulose.
 2. The method according toclaim 1, wherein the cellulose-containing material provided in step a)comprises at least 80 wt. % cellulose, preferably at least 90 wt. %. 3.The method according to claim 1, wherein the dry weight ratio betweencellulose-containing material and oxalic acid dihydrate is 1:1 to 1:100,preferably 1:1 to 1:50, more preferably 1:1 to 1:10, most preferably1:2.3 to 1:3.9.
 4. The method according to claim 1, wherein the reactionin step b) is solvent-free.
 5. The method according to claim 1, whereinthe cellulose-containing material and the oxalic acid dihydrate areheated above 106° C., in step b), preferably the cellulose-containingmaterial and the oxalic acid dihydrate are heated above 110° C., in stepb), more preferably the temperature in step b) does not exceed 120° C.6. The method according to claim 1, wherein the mixture is washed instep c) with at least one solvent capable of dissolving oxalic aciddihydrate, the mixture is washed in step c) with at least one selectedfrom the group consisting of ethanol, acetone, water, and THF.
 7. Themethod according to claim 1, wherein the suspension is prepared using atleast one selected from the group consisting of sonication,micro-fluidization, and mechanical disintegration, and wherein when thesuspension is prepared using micro-fluidization also nanofibrillatedcellulose is recovered.
 8. A composition comprising nanocrystallinecellulose manufactured according to claim 1, preferably saidnanocrystalline cellulose has free carboxyl groups with a density in therange 0.2-1.3 mmol/g, preferably 0.4-1.3 mmol/g.
 9. A method formanufacturing nanocellulose, said method comprising the steps of: a.providing a cellulose-containing material wherein thecellulose-containing material contains less than 20 wt. % water,preferably less than 10 wt. % water, b. contacting thecellulose-containing material with oxalic acid dihydrate, and heatingabove the melting point of the oxalic acid dihydrate, to obtaincellulose oxalates, wherein the dry weight ratio betweencellulose-containing material and oxalic acid dihydrate is 1:1 to 1:100,preferably 1:1 to 1:50, more preferably 1:1 to 1:10, most preferably1:2.3 to 1:3.9, c. washing the mixture resulting from step b), d.preparing a suspension comprising the washed material from step c),wherein the suspension is prepared using micro-fluidization, and e.recovering nanocellulose from the suspension, wherein said nanocelluloseis nanofibrillated cellulose.
 10. The method according to claim 9,wherein the cellulose-containing material provided in step a) comprisesat least 80 wt. % cellulose, preferably at least 90 wt. %.
 11. Themethod according to claim 9, wherein the reaction in step b) issolvent-free, preferably cellulose-containing material is not contactedwith a deep eutectic solvent(s).
 12. The method according to claim 9,wherein the cellulose-containing material and the oxalic acid dihydrateare heated above 106° C., in step b), preferably thecellulose-containing material and the oxalic acid dihydrate are heatedabove 110° C., in step b), more preferably the temperature in step b)does not exceed 120° C.
 13. The method according to claim 9, wherein themixture is washed in step c) with at least one solvent capable ofdissolving oxalic acid dihydrate, preferably the mixture is washed instep c) with at least one selected from the group consisting of ethanol,acetone, water, and THF.
 14. A composition comprising nanofibrillatedcellulose manufactured according to claim 9, preferably saidnanofibrillated cellulose has free carboxyl groups with a density in therange 0.2-1.3 mmol/g, preferably 0.4-1.3 mmol/g. 15.-20. (canceled) 21.Use of the composition comprising nanocellulose according to claim 8 inat least one of: automotive bio-based composites such as fiberglassreplacement for structural and non-structural uses, cement additives,wet-strength additives, dry-strength additives, wet-end additives suchas wet-end additives in packaging coatings and films, transparent filmsfor food packaging, polymer composite additives in composites, paper,electronic packaging, pharmaceutical excipients such as fillers, papercomposites with superior strength properties, hygiene and absorbentproducts, mechanically enhanced spun fibers and textiles, cosmeticexcipients such as filler, food additives, insulation for buildings suchas sound and/or heat barriers, aerospace composites, aerogels for oiland gas, pigments such as architectural pigments, coatings, hydrophobicand self-cleaning coatings, paints, dispersants, viscosity modulators,building materials such as structural composites, switchable opticaldevices, bone replacement, tooth repair medical composites, strainsensors, filters such as filtration of water and air, flexible displays,OLED displays, flexible circuits, printable electronics, conductivesubstrates, solar panels such as flexible solar panels, smart packaging,photonics, and drug delivery.
 22. Use of the composition comprisingnanocellulose according to claim 14 in at least one of: automotivebio-based composites such as fiberglass replacement for structural andnon-structural uses, cement additives, wet-strength additives,dry-strength additives, wet-end additives such as wet-end additives inpackaging coatings and films, transparent films for food packaging,polymer composite additives in composites, paper, electronic packaging,pharmaceutical excipients such as fillers, paper composites withsuperior strength properties, hygiene and absorbent products,mechanically enhanced spun fibers and textiles, cosmetic excipients suchas filler, food additives, insulation for buildings such as sound and/orheat barriers, aerospace composites, aerogels for oil and gas, pigmentssuch as architectural pigments, coatings, hydrophobic and self-cleaningcoatings, paints, dispersants, viscosity modulators, building materialssuch as structural composites, switchable optical devices, bonereplacement, tooth repair medical composites, strain sensors, filterssuch as filtration of water and air, flexible displays, OLED displays,flexible circuits, printable electronics, conductive substrates, solarpanels such as flexible solar panels, smart packaging, photonics, anddrug delivery.